1. Field of the Invention
This invention relates to a vehicle suspension system and more particularly to a passive vehicle suspension system which includes a shock absorber having a fluid cylinder and in which the suspension properties of the fluid cylinder change in response to wheel acceleration, pitch, roll, or other movements of the vehicle.
2. Description of the Prior Art
A typical suspension system for vehicles utilize a suspension coil and a shock absorber interposed between a vehicle body and the vehicle wheel. The suspension coil spring generally resists loads applied to maintain the vehicle body and the road wheel in a predetermined positional relationship to each other. The shock absorber is typically intended to damp or absorb vibrations transmitted between the vehicle body and the road wheel. In some instances, the suspension system may be further provided with a roll-stabilizer for suppressing vehicular rolling motion.
In the recent past, it has become popular to utilize actively controlled suspension systems to provide smoother rides and more positive handling stability for vehicles, particularly automotive vehicles. Such actively controlled suspension systems may include hydraulic circuits which sense vehicle and wheel movements and in response thereto, control the application of hydraulic fluid under pressure from a source thereof through a pressure control valve to the suspension system. The control is effected by introducing or draining the pressurized working fluid with respect to a working chamber or chambers in a portion of the suspension system. Such a control unit actively performs anti-pitching, anti-rolling, suppression of wheel bouncing and the like. Although typically such prior art control suspension systems utilize hydraulic fluid, in some instances, pressurized pneumatic fluid has also been used.
Irrespective of the fluid medium utilized when an active control suspension system is utilized, such systems contain a large number of moveable parts and typically include a pump which is driven by the vehicle engine so as to maintain the source of fluid under pressure thus degrading fuel economy and adding substantially to the cost of the vehicle. Typical of such prior art active control suspension systems for vehicles are those shown in issued U.S. Pat. Nos. 4,625,994, 4,801,155, 4,911,469, and 4,982,979.